The prior art contains a number of references in various contexts which relate to the present invention.
Previous attempts to solve the problem of manganese staining may be found in U.S. Pat. Nos. 4,129,423 and 3,303,104.
The preparation of the polymeric materials which are used in the present invention to control manganese staining is within the scope of the prior art. See, for example, U.S. Pat. Nos. 2,886,558 and 3,022,279 (partially hydrolyzed polyacrylamides); and U.S. Pat. No. 3,933,673 (related materials). These compounds have been used for ohter purposes, such as the following: partially hydrolyzed acrylamides as flocculating agents (U.S. Pat. Nos. 3,784,597, 3,864,323); and several similar materials as chelating agents (U.S. Pat. No. 4,085,060).
The prior art also teaches the incorporation of chelating agents in surfactant containing compositions. An example of these references is U.S. Pat. No. 3,933,673. Built surfactants also may fall into this category. The typical uses of such built compositions, particularly in the context of tableted compositions, are within the purview of the detergent bar art.
Chelating materials have also been used for some analogous uses, for example, as scale inhibitors, as toilet bowl cleaners, and as stabilizers which prevent decomposition of peroxide bleaches in the presence of metal ions. It should be noted, however, that most of these prior uses of chelating agents have involved chelating materials which are not adapted to the present situation, in which materials are required to inhibit manganese staining in an environment which contains oxidizing material, in particular hypochlorite. For example, EDTA (ethylenediaminetetraacetic acid) and its several salts are widely known as chelating agents, but are not desirable for use in the present invention because they are not stable with respect to hypochlorite solutions. Other nitrogen-containing chelating agents, such as nitrilotriacetic acid (NTA), have problems similar to that of EDTA. Still other chelating agents, while able to chelate manganese, do not preferentially chelate manganese so as to be effective in the presence of the much higher concentrations of calcium and magnesium ions typically found in many local water supplies. (A typical water supply may have 6 to 7 grains of hardness per gallon, or 110 ppm of calcium carbonate.) Also, much of the art does not teach that one must inhibit manganese staining before a stain occurs, since once the manganese stain forms it is very difficult to remove. Finally, many chelating agents, although able to chelate manganese, are less desirable for use in compositions which will be introduced into waste water, since they contain the polyphosphate ions which have been implicated in the eutrophication of inland watercourses. In some areas use of such materials is restricted by law. As a result, there is a need for a new material which is able to prevent manganese staining while avoiding the problems associated with polyphosphate chelating or building agents.